One-way clutch mechanisms and injector devices

ABSTRACT

An incrementing mechanism suitable for use in a medical injector device has a driving member ( 11, 23 ) rotatably and slidably mounted within a tubular body ( 10 ) and arranged to advance an elongate element ( 12 ) in one direction with respect to the tubular body ( 10 ). A one-way clutch is defined by a channel ( 21 ) extending along the element ( 12 ), a generally conical surface ( 24 ) formed internally on the driving member ( 23 ) and surrounding the element ( 12 ), a blocking clutch member ( 22 ) located in the channel ( 21 ) and engageable with the conical surface ( 24 ), and freeing means adapted to disengage the clutch by lifting the clutch member ( 22 ) out of engagement with the conical surface so as to disconnect the driving member ( 23 ) from the element ( 12 ). The freeing means comprises a pressure component ( 25 ) held against rotation with respect to the element ( 12 ) and arranged to engage the clutch member ( 22 ), a spring ( 27 ) acting on the pressure component ( 25 ) to urge it away from its clutch disengaging position, and two sets of inter-engageable teeth ( 30, 31 ) formed respectively around the driving member ( 23 ) and around the pressure component ( 25 ), whereby rotation of the driving member ( 11, 23 ) with respect to the pressure component ( 25 ) causes the teeth ( 30, 31 ) of the two sets to ride over each other. This successively lifts the pressure component ( 25 ) against the action of the spring ( 27 ) to move the clutch member ( 22 ) out of engagement with the conical surface ( 24 ) and then allows the spring ( 27 ) to move the pressure component ( 25 ) to a position where the clutch member ( 22 ) engages the conical surface ( 24 ).

[0001] This invention relates to automatic one-way clutch means for usein an incrementing mechanism having a driving member rotatably andslidably mounted within a tubular body and arranged to advance anelongate element in one direction with respect to the tubular bodywithin which the element also is mounted. In addition, in its preferredaspects this invention further relates to such an incrementing mechanismadapted for use in conjunction with an injector device to permit theaccurate dispensing of a required pre-set dose of a medicament, wheneverthe device is used. The invention further relates to an injector deviceper se.

[0002] In my EP-0673482-A, I have described and claimed an incrementingmechanism primarily intended for use with a hypodermic syringe, topermit the setting of a required dose of a medicament, such as insulin,whereafter the depression of plunger accurately dispenses the requireddose through a needle connected to the syringe. The entire disclosure ofthe specification of EP-0673482 is incorporated herein by this referencethereto, and reference may be made thereto (or WO 94/15120, on whichEP-0673482 is based) for a further description of the prior artmechanism.

[0003] Tests on and trials of the mechanisms described in EP-0673482have lead to further development of those mechanisms to give improvedoperating performance, greater reliability and dose dispensing accuracy.It has also been possible to simplify the manufacture of the mechanismsand hence reduce the manufacturing costs, without compromisingperformance. Further development has resulted in three distinct versionsof injector device incorporating the mechanisms—namely: (1) a disposableinjector which is discarded when a cartridge containing the medicamenthas been exhausted; (2) a reusable injector which can be reset when acartridge containing the medicament has been exhausted, so permittingthe replacement of the spent cartridge by a new one; and (3) arepeatable pre-set dose injector which permits the initial setting of arequired dose and thereafter can be used solely for the repeateddispensing of just that dose. All of these versions incorporate theimproved automatic one-way clutch means of this invention, for theincrementing mechanism forming the basis of the injector.

[0004] According to its broadest aspect, this invention provides anautomatic one-way clutch means for use in an incrementing mechanismhaving a driving member rotatably and slidably mounted within a tubularbody and arranged to advance an elongate element in one direction withrespect to the tubular body within which the elongate element also ismounted, which one-way clutch means comprises a channel extending alongthe element, a generally conical surface formed internally on thedriving member and surrounding the element, a blocking clutch memberlocated in the channel and engageable with the conical surface, andfreeing means adapted to disengage the clutch by lifting the clutchmember out of engagement with the conical surface so as to disconnectthe driving member from said element, which freeing means comprises apressure component held against rotation with respect to the element andarranged to engage the clutch member, a spring acting on said componentto urge the component away from its clutch disengaging position, and twosets of interengageable teeth formed respectively around the drivingmember and around the pressure component whereby rotation of the drivingmember with respect to the pressure component successively lifts saidcomponent against the action of the spring to move the clutch member outof engagement with the conical surface and allows the spring to move thepressure component to a position where the clutch member engages saidsurface, through the interaction of the teeth riding over each other.

[0005] Though the one-way clutch mechanism of this invention could beused for purposes other than as a part of an injector device of the kinddescribed hereinbefore, the primary intention is for the mechanism to beincorporated in such an injector. The invention will therefore behereinafter described expressly with reference to that use, though itwill be understood that the invention is not to be regarded as limitedto that use.

[0006] The mechanism described in EP-0673482 has a one-way clutchincluding a generally conical surface 23 formed on a driving member(plunger 11), spring 25 bearing on a washer 24 to urge balls 22 intotheir active position. On rotating the driving member with respect tothe elongate element (rod 12), internal walls 27 within the conicalsurface 23 serve to move the balls 22 away from their active positions,against the action of spring 25. This arrangement has the disadvantagethat very tight tolerances are required during manufacture and also thenumber of times the clutch could be released on a full rotation of thedriving member is severely limited. The consequence of this is that theread-out numerals for a set dose must be of a small height. A practicalexample of the earlier design allowed 4 released positions with amaximum of 12 on a full revolution of the driving member; and with eachdose needing a forward movement of 0.138 mm of the elongate element (rod12) the maximum numeral size was 1.656 mm.

[0007] In the mechanism of this invention, the generally conical surfacemay be substantially, or wholly, continuous, uninterrupted by the walls27 of the previous design. This allows very many more clutch-releasedpositions for each revolution of the driving member. A current preferreddesign has, in each set, teeth at 20° stations around the circumferenceand this results in a maximum numeral size of 2.484 mm. By positioning alens over the window in the body through which the numerals are read,that may be increased to an effective height of over 4 mm.

[0008] It is highly preferred that the pressure component isadditionally configured to urge the clutch member to its active,conical-surface engaging position. To this end, the teeth on the drivingmember and on the pressure component should be configured so that theydo not fully interengage when meshed, so that the pressure component maystill exert force on the clutch member. In turn this serves to ensurethat there is a minimum of backlash between the driving member and theelongate rod, when the driving member is pressed in the one direction,which drives the elongate element to dispense a dose of medicament, whenthe mechanism is incorporated in an injector.

[0009] As with the previous design, it is preferred for there to be twodiametrically opposed clutch members so as uniformly to distribute theforces, though it is possible a single clutch member could be employed.Each clutch member could be a wedge form integral with the pressuremember, a floating wedge form or a conical roller, but preferably is aball, located in a suitably shaped channel in the elongate element, soas to effect driving of that element upon depression of the drivingmember (the plunger, of the previous design).

[0010] In the previous design of injector, as described in EP-0673482, ahelix (thread form) was formed in the internal surface of the tubularbody and was engaged by a follower on the driving member such thatrotation of the driving member threaded that member backwardly topre-set a dose. Preferably, the design is reversed, so that the helix isnow formed on the driving member, which carries the one-way clutchmechanism, and a follower is provided on the tubular body. In this case,the one-way clutch mechanism may be formed as a separate unit linked tothe main part of the driving member by means of a lost motion mechanism,permitting a limited amount of axial movement between the two componentsbut holding the two elements against relative rotational movement. Thisarrangement permits an annular groove to be formed at one end of thehelix and in which the cam follower is disposed before the mechanism isset to dispense a dose. A spring loading applied to the driving memberurges the follower to engage in the helix at the start of rotation ofthe driving member, to set the mechanism to its ‘zero’ position. Theaxial movement of the driving member to reach this position should beaccommodated by the lost motion mechanism, with the mechanism thenpulling the one-way clutch on further advancement of the driving memberupon the rotation thereof.

[0011] Preferably, the mechanism includes means to prevent the selectionof a dose for injection which is greater than the remaining dose in acartridge of medicament coupled to the injector. Such means may includea coupler connected to the driving member and disposed about theelongate element, the coupler having projections which are engageablewith an abutment at the end of the element. During the movement of thedriving member away from its starting position by the rotation thereof,the coupler will move with that driving member but when the projectionon the coupler engages the abutment on the end of the element, thecoupler then prevents further axial movement of the driving member. Inthis way, once the maximum remaining dose in a cartridge has beenselected, no greater dose may be set on the driving member, fordispensing.

[0012] An injector incorporating the mechanisms of the invention asdescribed above may be arranged to allow the dispensing of a singlecartridge of medicament, whereafter the entire injector is disposed ofsince the mechanism cannot be reset. In the alternative, the injectormay permit the replacement of a spent cartridge by a fresh, fullycharged cartridge, but in this case the mechanisms must permit thereturn of the elongate rod to its initial position, against the actionof the one-way clutch mechanism and a further non-return clutch alsoincorporated in the injector as described in EP-0673482. Preferably, inthe latter case, the disengagement of the cartridge from the main bodyof the injector automatically releases the further non-return clutch, sopermitting the elongate element to be pushed back to its startingposition, either manually or by the piston of a fresh cartridge, as thecartridge is offered to the injector and is secured thereto.

[0013] A modification of either form of the injector permits it todispense repeated doses of up to a pre-set volume (number of units) lessthan the maximum volume which the injector is capable of dispensing. Thepre-set maximum dose is selected by turning the driving member in theappropriate sense until a friction clutch starts slipping, whereafterthe driving member is thrust forwardly to dispense the dose.

[0014] By way of example only, several specific embodiments of injectorincorporating an incrementing mechanism of this invention will now bedescribed, reference being made to the accompanying drawings, in which:

[0015] FIGS. 1 to 7 show a first embodiment of injector;

[0016]FIGS. 8 and 9 show a second embodiment, in the form of adisposable mechanism;

[0017]FIG. 10 shows a modified form of the second embodiment, again inthe form of a disposable mechanism; and

[0018]FIGS. 11 and 12 show a third embodiment having a side button torelease the mechanism.

[0019] In more detail:

[0020]FIG. 1 is an exploded isometric view showing the individualcomponents of the first embodiment;

[0021]FIGS. 2A, 2B and 2C respectively show three alternative clutchmechanisms, the mechanism of FIG. 2C being used in the embodiment shownin FIG. 1 and in each case, the Figure showing both an expandedisometric view and an assembled cut-away view;

[0022]FIG. 3 is a partially cut-away isometric view of the assembledinjector of FIG. 1;

[0023]FIG. 4 is an axial section through the mechanism of FIGS. 1 and 3;

[0024]FIGS. 5A and 5B are respectively isometric and axial sectionsthrough the plunger and components associated therewith;

[0025]FIG. 6 shows in more detail the helix on the plunger and thefollowers which co-operate therewith;

[0026]FIG. 7 shows a further one-way clutch mechanism used in theinjector of FIGS. 1 and 3;

[0027]FIG. 8 is an exploded isometric view showing the individualcomponents of the second embodiment;

[0028]FIG. 9 is an axial section through the mechanism of FIG. 8;

[0029]FIG. 9A is an isometric end view on a part of the mechanism ofFIG. 9;

[0030]FIG. 10 is an axial section through a modified form of themechanism of FIG. 8;

[0031]FIG. 10A is an isometric end view on a part of the mechanism ofFIG. 10;

[0032]FIGS. 11 and 12 are axial sections through a third embodiment,respectively when set to perform an injection and having performed aninjection; and

[0033]FIGS. 13A and 13B are detail partial views on the releasemechanism of the third embodiment.

[0034] In the following description, references to “forwardly” and“rearwardly” are intended to refer to the normal disposition of aninjector and thus the forward end thereof is that carrying a needlewhich performs the injection and the rearward end is that which isdepressed, to dispense a dose of medicament. In the Figures, the forwardend is that shown on the left and the rearward end that shown on theright.

[0035] Referring initially to FIGS. 1 to 7, the injector comprises atubular body 10 within which is mounted a plunger 11 and a co-axialelongate rod 12 for acting on the piston 13 (FIG. 4) of a cartridge ofmedicament, located within a cartridge holder 19, held to the body 10 bya bayonet connection.

[0036] The plunger 11 is generally tubular and has at its rear end anend-cap 14 connected to the plunger through a friction clutch includingspring 15, which clutch slips in the event that a rotating force isapplied to the end-cap 14 and which rotation cannot be transferred tothe plunger for reasons to be described below. Slidably received withinthe plunger 11 is the rod 12, a washer 16 being mounted on its forwardend to give a large area to contact piston 13. At the rearward end, therod 12 has a stop 17, for a purpose to be described below.

[0037] At the forward end of the plunger 11, there is provided anautomatic one-way clutch mechanism 18 shown in more detail in FIGS. 2,4, and 5B and which serves to couple the plunger 11 to the rod 12 whenthe plunger is driven forwardly (to the left) in the direction of arrowA but allows the plunger 11 to be moved rearwardly in the direction ofarrow B, whilst the rod 12 remains stationary.

[0038] The rod 12 has a generally H-shaped cross-section defining twochannels 21 in each of which is located a respective ball 22. The clutchmechanism includes a cone member 23 defining an internal conical surface24 overlying the balls 22, such that on forward movement of the conemember 23, the balls 22 are jammed in the space between the cone memberand rod, so coupling the cone member to the rod. On rearward movement ofthe cone member, the balls may roll to a wider part of the space betweenthe cone member and the rod, thus disconnecting the cone member and therod.

[0039] A pressure component 25 is slidably arranged on the rod 12 andextends through the cone member 23, the pressure component having at itsrearward end an opposed pair of upstanding ribs 26. A compression spring27 acts between those ribs and a shoulder in the cone member, sothrusting the pressure component to the right with respect to the conemember (FIG. 4). The pressure component has a pair of opposed radialsockets 28 with the balls 22 located in those sockets; movement of thepressure component 25 to the left against the action of spring 27 thusfrees the one-way clutch mechanism, whereas movement of the pressurecomponent to the right under the action of the spring 27 urges the ballsinto the gap between the conical surface and the rod, so engaging theclutch mechanism 18.

[0040] Around the forward end of the cone member 23 are formed axiallyprojecting teeth 30, the pressure component 25 having a flange on whichare formed generally similar teeth 31 inter-engageable with the teeth30. Rotation of the cone member 23 thus will cause the teethrespectively on the cone member and the pressure component to overrideone another, so alternately lifting the pressure component against thespring bias, and allowing the spring bias to jam the balls between theconical surface and the rod. The teeth are formed such that they do notfully inter-engage, so ensuring that the sockets 28 always apply aspring load on the balls, when the pressure component has not beenlifted by the teeth.

[0041] The outer surface of the cone member 23 has a pair of opposedlugs 33 which are received in corresponding slots 34 in the plunger 11.The slots and lugs are configured so that there is essentially norotational backlash between the two components though there is lostaxial motion between the cone member and the plunger, controlled bycatches 35 on the cone member and received in apertures 36 in theplunger.

[0042] Rearwardly of the clutch mechanism 18, the plunger 11 is formedwith an external precision helix 37 (see particularly FIGS. 3 and 6), ineffect having a toothed form and which is engaged by three cam followers38 resiliently movable in the radial direction. The followers are formedas a separate component 39 secured to the tubular body 10; each followeris in the form of an arm 40 projecting from that component 39 and havingat its forward end a chamfered tooth 41 engageable in the helix.Further, the follower teeth 41 are arranged on the same helical pitch asthe helix 37 on the plunger. The component 39 also defines a window 42into which is fitted a magnifying lens 43, positioned within a cover 44.A spring-assistor 38A is arranged between the cover 44 and the followers38 to ensure adequate engagement with the helix 37.

[0043] A coupler 45 is located partially within the plunger 11 and isarranged to prevent setting of the injector to a dose greater than thatremaining within a connected cartridge. Spring 46 acts between a flange47 on the coupler 45 and an internal shoulder 48 of the plunger (FIG. 4)so as to urge the coupler forwardly, whilst simultaneously urging theplunger rearwardly. The flange 47 engages the rear face of the conemember 23, the coupler having a pair of arms 49 projecting forwardlywithin the pressure component 25 and having hook-shaped forward ends.These forward ends are engageable by the stop 17 on rod 12, so as toprevent further rearward movement of the plunger once so engaged.Further, the forward ends engaging the stop 17 prevent the rod 12 beingpulled forwardly out of the assembly when no cartridge is present.

[0044] The plunger has a cylindrical external surface 50 between thehelix 37 and its rearward end, on which surface are marked in a helicalfashion numerical indicators of the dose to be dispensed followingsetting of the mechanism. The set dose is viewable through the lens 43located in the window 42.

[0045] The rearward end of the helix 37 runs into an annular groove 51in which the teeth 41 of the followers 38 are received when the injectoris in its initial setting. Referring particularly to FIGS. 5A and 6,there are upstands 52 in the annular groove 51 aligned with valleysbetween the teeth of the helix 37, at the zero position of the plunger.On rotating the plunger 11 by means of the end-cap 14 in the correctsense (clockwise, when viewed from the rear end), the spring 46 urgesthe plunger 11 to the right so permitting the teeth 41 of the camfollowers to engage into the helical thread when all three followerteeth are on their respective upstands 52 in the groove 51, thisoccurring at the zero position of the plunger. The chambers on therespective teeth facilitate the engagement of the follower teeth 41 intothe helix 37.

[0046] Initially, with the teeth 41 in the annular groove, a coloredband is visible through window 42 but when the followers engage thethread, at the zero position, the numeral ‘0’ is visible through thewindow. Continued rotation of the end-cap 14 winds the plunger 11further to the right, with the selected dose visible through the windowincrementing as this continues. Once the set dose has been achieved, aconnected needle 53 is inserted into a suitable site and the end-cap 14depressed to effect dispensing of the selected dose. This is achieved bythe plunger pushing the cone member 23 to the left, the one-way clutchmechanism 18 coupling the leftward movement of the cone member 23 to therod 12, the forward end of which bears on the piston 13 of a connectedcartridge of medicament, so moving the piston to dispense thatmedicament. Movement of the plunger 11 is continued until the outer edgeof the cone member 23 engages an abutment 54 formed on an internal wallwithin the body 10 and through which the rod 12 passes in a slidable,but non-rotatable, manner.

[0047] During the driving of the plunger 11 to the left, the teeth 41 ofthe cam followers 38 ride over the parts of the helix having arelatively low angle; but when the plunger is set between doses, theplunger cannot be driven to the left by virtue of the profile of thehelix. Moreover, the rear wall of the helix is relatively sharp, so thatthe followers prevent the plunger being pulled rearwardly.

[0048] As the dose is being set, the cone member 23 rotates with respectto the pressure component 25, so lifting that component each time theteeth ride over each other, as described above. This also has the actionof freeing the clutch between the set doses and thus there is no penaltyin over-shooting the required dose and then winding the end-cap 14 inthe opposite sense, from a larger dose to a lesser dose, since this willnot significantly drive the rod 12 forwardly.

[0049] During movement of the plunger 11 to the right, by rotation ofthe end-cap 14, the rod 12 is held against rearward movement by afurther one-way clutch mechanism 55, provided forwardly of the internalwall defining abutment 54. This clutch mechanism 55 has a check member56 with two integrally hinged wedges 57 located in the channels 21 ofthe rod 12 and around which is disposed a locking component 58 theinternal profile of which drives the wedges 57 into engagement with therod 12—see particularly FIG. 7. In the normal loaded position shown inFIG. 3, the wedges 57 serve as a one-way clutch to prevent rearwardmovement of the rod 12, whilst permitting free forward movement of thatrod. The locking component 58 is coupled to the pressure component 25 bylegs 59 projecting forwardly from that component through slots (notshown) formed in the internal wall in the tubular body 10. The lockingcomponent 58 is engaged with a tubular key 60 by means of clips 61located in holes 62 in the key 60.

[0050] The key forms a part of a bayonet locking mechanism for thecartridge holder 19, as well as controlling action of the further clutchmechanism 55. The cartridge holder 19, containing a cartridge ofmedicament, is loaded by pushing the cartridge holder rearwardly withrespect to the body 10 to engage the bayonet slots of the holder withlugs 10A formed internally within the forward end of the body 10.Twisting the holder to complete the bayonet connection turns the key 60,which rotates the locking component 58 to bring check member 56 intoengagement with rod 12. This releases the pressure component 25 frombeing pulled forward, so that dose setting can subsequently beperformed. Removal of the cartridge holder by releasing the bayonetconnection re-sets the key 60 to pull forward the pressure component 25and so free the check member 56; in turn this allows the rod 12 to bepushed rearwardly back to its initial position.

[0051] Cams 63, formed on the external surface of the locking component58, prevent rotation of that component until aligned with the recesses64, so that cartridge replacement cannot take place until the plunger 11is in its forward position. Turning the key 60 on disconnecting thecartridge holder also pushes the check member 56 away from lockingcomponent 58 through further inter-engaging cam surfaces 65 and 66against the action of internal spring 67, thereby releasing the wedges57 from the locking component 58. Rod 12 can now be moved in eitherdirection and may be pushed rearwardly, either manually or by the piston13 of a fresh cartridge, ready to dispense a new dose.

[0052] The above described embodiment uses a one-way clutch mechanism 18as shown in FIG. 2C. However, that mechanism could take other forms,such as shown in FIGS. 2A or 2B. In FIG. 2, like parts are given likereference numbers. In FIG. 2A, the pressure component has wedges 69formed integrally therewith, on resilient arms 70. The profile of thechannels 21 in rod 12 may need to be modified so as to suit thesewedges. In the arrangement of FIG. 2B, the wedges 69 are formedseparately and are received in apertures 71 in the pressure component. Afurther possibility would be to provide rollers of a somewhat conicalform so as to give a three line contact. These arrangements may be morepreferred than the use of balls, as shown in FIG. 2C, to avoid highpoint loadings on the conical surface 24 of the cone member 23 and onthe rod 12, which could lead to dimpling of that surface 24 and rod 12.

[0053] The injector of FIGS. 8 and 9 differs from that of FIGS. 1 to 7in that the one-way clutch mechanism 18 is simplified and uses only oneball, rather than the two balls of FIGS. 1 and 2C. The further one-wayclutch mechanism 55 is omitted and is replaced by a simple lockingwasher 73 (see particularly FIG. 9A) to prevent rearward movement of therod 12. Also, the end cap arrangement is modified in that spring 15 isomitted; rather an integral spring is formed with the modified end cap14A. In other respects the injector corresponds to the first embodimentdescribed above. Consequently, like parts are given like referencecharacters and will not be described again here.

[0054] The locking washer 73 is of pressed spring steel and has aninwardly projecting tooth 74 which locates in the channel 21 of the rod12, forwardly of the internal wall of the tubular body 10. The washeralso has two or more inwardly projecting arms 75 which are pushed intoengagement with a raised boss 76 on the forward face of the internalwall, as shown in FIGS. 9 and 9A. As best seen in FIG. 9, the tooth 74is deformed forwardly by the action of fitting the washer on the rod;any attempt to move the rod rearwardly is resisted by that tooth,digging into the material of the rod. As described above, a dose isdispensed by moving the plunger 11 and also the rod 12 forwardly, whichmovement of the rod is permitted by the washer 73. Once a connectedcartridge is empty, the entire mechanism cannot be re-used since the rodcannot be moved back to its initial position and so the mechanism isscrapped.

[0055] The modified end cap 14A has axially-projecting resilient fins 77which engage internal ribs within the plunger 11, but when the plungercan no longer rotate, the fins 77 will ride over the ribs should caprotation be continued. The cap itself is held on the plunger by anintegral key received in a peripheral groove 11A adjacent the rear endof the plunger 11 (FIG. 9).

[0056]FIGS. 10 and 10A show a modified form of the second embodiment,differing in that the one-way clutch mechanism 18 is of the same form asthat of the first embodiment, and so having two balls 22 disposed inopposed channels 21 in the rod 12. This allows the use of a lockingwasher 78 having a pair of opposed teeth 79 fitting into the twochannels respectively, of the rod. In other respects, the locking washer78 operates in much the same manner as the locking washer 73 and willnot be described further, here.

[0057] This modified second embodiment also includes a pre-settingfacility. Some drugs may be prescribed according to body weight, age andso on, with the intention of a defined dose being given at regulartimes. For this purpose, the plunger 80 of this modified embodimentdiffers from plunger 11 and the rearward end of the injector is providedwith a pre-set lock arrangement which permits the setting of a dose nogreater than the pre-set amount. This pre-set lock arrangement includesa button 81 engageable with a rotatable ring 82 threadingly engaged witha pre-set stop 83, disposed around a central tubular portion 84 of theplunger 80. The end-cap 14 is also modified so as to include a centralprojection 85, rotatably connecting the cap to the central portion 84.

[0058] In use, pre-setting is performed by initially winding the end-cap14 until the required dose is shown through window 42. The button 81 isthen depressed which frees ring 82 for rotation; this is rotated untilthe pre-set stop 83 engages end-face 86 of the outer part 87 of theplunger 80, also carrying the dose numerals. The button 81 is thenreleased so locking the ring 82. Thereafter, rearward movement of theplunger 80 is limited by the pre-set stop 83, to the maximum requireddose and in the event that the end-cap 14 is further rotated, it willsimply slip with respect to the plunger 80.

[0059] If the remaining dose in a cartridge is less than the pre-setdose, the plunger cannot be wound out to the pre-set dose by virtue ofthe inter-action of the arms 49 of the coupler 45 with the stop 17 onrod 12, as has been described above. The maximum available dose willthen be displayed through the window 42.

[0060] The third embodiment, shown in FIGS. 11, 12, 13A and 13B, differsfrom the previous embodiments in that no plunger is provided fordispensing the dose. Instead of winding out the end-cap 14 and pressingthe plunger home to deliver the medicament, the user rotates the end-capuntil the desired dose appears in the window. After pushing the needleinto the appropriate site, the user presses a side release button andthe medicament is injected without further user participation, under theaction of an internal spring. Apart from the changes required to themechanism to give the above functionality, the mechanism is similar tothe previous embodiments and insofar as is possible, like components aregiven like reference characters.

[0061]FIG. 12 shows the mechanism at its zero position and FIG. 11 whenset to dispense a dose of medicament, immediately after release of themechanism but before dispensing has commenced.

[0062] End-cap 90 is permanently snapped on to the rearward end of thetubular body 10. The end-cap has external splines 91 which engage withinternal splines 92 on a track member 93 mounted both for rotation andaxial movement within the tubular body 10. This track member defines aprecision helix 94, corresponding to helix 37 on plunger 11, but herethe helix is unbroken and the follower is in the form of a tooth 95formed integrally with a side release button 97 pivoted to the body 10.The button is urged by an integral leaf spring 102 to the position shownin FIGS. 12 and 13B where the tooth is engaged with the helix.. A spring96 acting between the end-cap 90 and an internal shoulder in the trackmember 93 urges that track member to the left, the internal shoulderalso engaging a coupler 45 having the same function as has beendescribed above.

[0063] The side release button 97 co-operates with an interlock 98 , toensure the button 97 remains in its released position (FIGS. 11, 13A)once depressed, until an injection has been completed. The interlock 98is urged rearwardly by a spring 100 within the button 97 acting onabutment 101 of the interlock, but is held against the action of thatspring by the rearward edge of extension 103 of the interlock engagingthe tooth 95, until the button is depressed. Then, the extension 103 ofthe interlock moves between the tooth 95 and the track member 93 underthe action of spring 100, so preventing re-engagement of the tooth withthe helix. On the track member being moved forwardly under the action ofspring 96, the interlock is also moved forwardly by the track member,until the tooth 95 may once more drop into the track, moving the buttonoutwardly under the action of spring 102, assisted by spring 100.

[0064] On turning the end-cap 90, the track member 93 is threadedrearwardly, until the required dose is visible through window 42. Then,on depressing the button 97, the tooth is released from the track, sopermitting an injection to be given by the track member being thrustforwardly by spring 96.

[0065] In other respects, the mechanism is essentially similar to thatof the previous embodiments; for example, it may be made as a re-usabledevice or as a disposable device. As the action is similar to thatdescribed above, it will not be described in further detail here.

1. An automatic one-way clutch means for use in an incrementing mechanism having a driving member rotatably and slidably mounted within a tubular body and arranged to advance an elongate element in one direction with respect to the tubular body within which the elongate element also is mounted, which one-way clutch means comprises a channel extending along the element, a generally conical surface formed internally on the driving member and surrounding the element, a blocking clutch member located in the channel and engageable with the conical surface, and freeing means adapted to disengage the clutch by lifting the clutch member out of engagement with the conical surface so as to disconnect the driving member from said element, which freeing means comprises a pressure component held against rotation with respect to the element and arranged to engage the clutch member, a spring acting on said component to urge the component away from its clutch disengaging position, and two sets of inter-engageable teeth formed respectively around the driving member and around the pressure component whereby rotation of the driving member with respect to the pressure component successively lifts said component against the action of the spring to move the clutch member out of engagement with the conical surface and allows the spring to move the pressure component to a position where the clutch member engages said surface, through the inter-action of the teeth riding over each other.
 2. Clutch means as claimed in claim 1, wherein the generally conical surface is substantially, or wholly, continuous.
 3. Clutch means as claimed in claim 1 or claim 2, wherein the pressure component is additionally configured to urge the clutch member to its active, conical surface engaging position.
 4. Clutch means as claimed in claim 3, wherein the teeth respectively on the driving member and on the pressure component do not fully inter-engage when meshed, whereby the pressure component still exerts force on the clutch member when the teeth are meshed.
 5. Clutch means as claimed in any of the preceding claims wherein there are two diametrically opposed similar clutch members, each acting between the conical surface and the elongate element.
 6. Clutch means as claimed in any of the preceding claims wherein the or each clutch member comprises one of a ball, a roller, and a wedging member.
 7. An incrementing mechanism comprising a tubular body, a driving member slidably and rotatably mounted within the tubular body, an elongate element slidably mounted within the driving member and one way clutch means as claimed in any of the preceding claims and arranged to effect coupling between the driving member and the elongate element when the driving member is moved in one direction with respect to the tubular body, and arranged not to drive the elongate element when the driving member is moved in the other direction with respect to the tubular body.
 8. An injector device whenever incorporating an incrementing mechanism as claimed in claim 7, to effect incremental advance of the elongate element thereby to effect dispensing of a dose of medicament by virtue of inter-action between the elongate element and the piston of a medicament dispensing syringe or cartridge.
 9. An injector device as claimed in claim 8, wherein there is a further one-way clutch mechanism arranged between the tubular body and the elongate element, to resist movement of the elongate element in said other direction.
 10. An injector device as claimed in claim 9, wherein the further one-way clutch mechanism is selectively releasable to permit resetting of the incrementing mechanism to an initial position.
 11. An injector device as claimed in claim 12, wherein the selective releasing of the further one-way clutch mechanism is performed automatically by disconnecting a syringe or cartridge from the injector mechanism.
 12. An injector device as claimed in claim 8, wherein there is provided a non-resettable ratchet arrangement between the tubular body and the elongate element, whereby the injector device must be disposed of following full movement of the elongate element in a dose-dispensing direction.
 13. An injector device as claimed in claim 12, wherein the ratchet arrangement comprises a spring blade bearing on the elongate element and deflected in the direction of advancement of the elongate element.
 14. An injector device as claimed in any of claims 8 to 13, wherein there is a dose pre-setting arrangement which permits the pre-setting of a maximum dose to be dispensed less than the dose which otherwise could be pre-set on the mechanism.
 15. An injector device as claimed in claim 14, wherein the dose pre-setting arrangement includes a pre-setting ring threadingly coupled to a pre-setting lock slidably mounted within the tubular body and with which the driving member engages on being moved to pre-set the dose.
 16. An injector device as claimed in claim 15, wherein a locking arrangement is provided for the pre-setting ring.
 17. An injector device as claimed in any of claims 8 to 16, wherein there is provided means to restrict the setting movement of the driving member to a dose not greater than the remaining dose within a syringe or cartridge connected to the device.
 18. An injector device as claimed in claim 17, wherein said restricting means includes an abutment engageable with a stop at or adjacent the elongate element remote from a connected syringe or cartridge which abutment is rotatably coupled to the driving member.
 19. An injector device as claimed in any of claims 8 to 18, wherein the driving member is provided with an end-cap by means of which the driving member is turned to move the driving member in the other direction and by means of which the driving member is depressed in the one direction.
 20. An injector device as claimed in any of claims 8 to 18, wherein the driving member is coupled to an end-cap to permit the rotation of the driving member thereby to move the driving member in the other direction, the driving member being spring-urged to move in the one direction and being provided with a releasable catch to hold the driving member against movement in the one direction, until released. 